@book{dspguide,
   title = "The Scientist and Engineer's Guide to Digital Signal Processing",
   author = "S. W. Smith, Ph.D.",
   publisher = "California Technical Publishing",
   year = "1997"
   }
   
@inbook{fourierbook,
   title = "Fourier Analysis for Beginners",
   author = "L.N. Thibos",
   chapter = "12",
   publisher = "Visual Sciences Group",
   year = "2003"
   }
   
   @inbook{signsyst,
   title = "RES.6-007 Signals and Systems",
   author = "Oppenheim, A. V.",
   chapter = "9",
   publisher = "Massachusetts Institute of Technology: MIT OpenCourseWare",
   year = "2011",
   note = "http://ocw.mit.edu (Accessed 22 Nov, 2012). License: Creative Commons BY-NC-SA"
   }
   
@UNPUBLISHED{audio_speech,
   author = "Lic. Ing. D. Van Landeghem",
   title = "{Introduction to audio and speech processing}",
   year = 2008
   }